Via did well with the release of the Unichrome driver, but have blown it since with their lack of support for further development. Most of the new Via Unichrome chipsets are not fully supported because of a lack of details from Via & S3.

S3 are even worse in this regard with no open Deltachrome or Gammachrome drivers at all. It's very poor, especially as the previous generation (Savage) was so well supported.